1. Technical Field
The present invention relates to a data storage medium such as an optical disc, which can be used effectively to guarantee appropriate copyright protection, and a read drive for use to read the medium.
2. Background Art
Disk storage media, on which various types of data (or information) can be stored, include read-only data storage media and recordable data storage media.
Generally speaking, in the past, read-only drives for reading data that was written on read-only data storage media were popularized first, and then optical disc drives for writing data on recordable data storage media or reading the data that was written on recordable data storage media were popularized. Accordingly, to make the recordable data storage media also readable by the read-only drives, the physical dimensions (including the diameter and thickness of discs), physical properties (such as reflectance) and data recording format of the recordable data storage media were matched with those of the read-only data storage media as closely as possible. As a result, however, even copyrighted data, recorded on a read-only data storage medium, may be easily copied onto a recordable data storage medium. Thus, the copyright of such data has often been infringed.
To avoid this unwanted situation, various techniques of discouraging illegal duplication have been developed and used in the field of optical discs. Hereinafter, a conventional technique of discouraging such illegal duplication will be described with reference to FIGS. 1 through 3.
First, a conventional recordable data storage medium will be described with reference to FIG. 1. Modulated property data 15 is recorded on a recordable data storage medium 1 during the manufacturing process thereof before the storage medium 1 is put on the market. The modulated property data 15 is obtained by getting property data 4 (i.e., information unique to each storage medium) modulated by a modulating section 16. The property data 4 may be a disc ID, for example.
A user who bought the recordable data storage medium 1 can write the data 6 (to be stored in the removable storage medium) on the user area of the recordable data storage medium 1 or read the data 6 from the user area by using an optical disc drive.
Such an apparatus that can write the data on the recordable data storage medium 1 and/or read the data from the medium 1 (i.e., the optical disc drive) includes a demodulating section 17 for demodulating the modulated property data 15 that was recorded on the recordable data storage medium 1 and a decrypting section 10 for decrypting encrypted data 2 that has also been written on the recordable data storage medium 1.
Where the user writes the encrypted data 2 on the recordable data storage medium 1, the data 6 is converted into the encrypted data 2 (e.g., scrambled data) by an encrypting section 7 inside the optical disc drive and then written on the recordable data storage medium 1. The modulated property data 15 that has been recorded in advance on the recordable data storage medium 1 is used for this encryption. More specifically, before the data 6 is encrypted, the modulated property data 15 is read out from the recordable data storage medium 1 and then demodulated by the demodulating section 17. Thereafter, the encrypted data 2 is generated from the data 6 by using the demodulated property data 15.
In reading the data from the recordable data storage medium 1, first, the modulated property data 15 is read and then demodulated into the property data 4 by the demodulating section 17. Next, the encrypted data 2 is read from the user data area on the recordable data storage medium 1 and then transmitted to the decrypting section 10, where the encrypted data 2 is decrypted by using the demodulated property data 4.
Next, a read-only data storage medium will be described with reference to FIG. 2.
After encrypted data 2, modulated property data 15 and recorded encryption data 12 have been recorded on a read-only data storage medium 14 during the manufacturing process thereof, the read-only data storage medium 14 is shipped. The modulated property data 15 is obtained by getting the property data 4 (i.e., information unique to each storage medium) modulated by the modulating section 16.
The encrypted data 2 is generated by encrypting the data 6 with a cryptographic key. This cryptographic key is generated by using encryption data 11. The data 6 to be copyrighted is encrypted with the cryptographic key into the encrypted data 2, which is then recorded on the read-only storage medium 2.
The encrypted data 2 and the recorded encryption data 12 are recorded on different areas on the storage medium during the manufacturing process thereof. The modulated property data 15 may not be recorded on the read-only data storage medium 14. In a DVD-ROM, for example, the recorded encryption data 12 includes cryptographic key information for use in a contents scrambling system (CSS), and the encrypted data 12 is obtained by scrambling the contents of the data 6 in accordance with the information.
A user who bought the read-only data storage medium 14 can decode the encrypted data 2 by using a regular read drive. The read drive for reading such a read-only data storage medium 14 includes: a demodulating section 17 for demodulating the modulated property data 15 that was recorded on the read-only data storage medium 14; a decrypting section 10 for decrypting the encrypted data 2 that was recorded on the recordable data storage medium 1; a type recognizing section 8 for determining whether the storage medium to read is a read-only data storage medium or a recordable data storage medium; and a switch 13 for prohibiting or allowing the use of the recorded encryption data 12 in accordance with the result obtained by the type recognizing section 8.
FIGS. 3(a) through 3(c) are schematic representations showing a physical difference between the read-only data storage medium and the recordable data storage medium. Specifically, FIG. 3(a) illustrates tracks of the read-only data storage medium, FIG. 3(b) illustrates recording tracks of the recordable data storage medium, and FIG. 3(c) illustrates a broader area including the portion shown in FIG. 3(b).
On the read-only data storage medium, pits 51 are formed on the data recording tracks 50 as shown in FIG. 3(a). On the recordable data storage medium on the other hand, recording marks 53 are formed on grooves 52 functioning as data recording tracks as shown in FIG. 3(b). As used herein, the “recording marks” 53 are portions of a recording film, of which the properties (e.g., reflectance) have been changed through the exposure to a laser beam.
On a recordable data storage medium such as a DVD-R or a DVD-RW, pits 54 are formed on a land portion between the grooves 52 and the grooves 52 slightly wind in a regular period and within a predetermined amplitude as shown in FIG. 3(c). Such winding of the grooves 52 is called “wobbling”. No track wobbling like this is observed on any read-only data storage medium.
By detecting the groove wobbling such as that shown in FIG. 3(c), the type recognizing section 8 of the read drive can determine whether the storage medium to read is a read-only data storage medium or a recordable data storage medium. A detector that may be used as such a type recognizing section 8 is disclosed in U.S. Pat. Nos. 5,459,706 and 6,088,307, which are hereby incorporated by reference.
As shown in FIG. 2, the encrypted data 2, which has been read out from the read-only data storage medium 14, is decrypted by the decrypting section 10 using the recorded encryption data 12. In this case, the type recognizing section 8 senses that the data storage medium being read is a read-only data storage medium and turns the switch 13 ON. If necessary, the modulated property data 15 is demodulated by the demodulating section 17 and used.
Next, it will be described what if one tries to read the recordable data storage medium 1, onto which the encrypted data 2 and the recorded encryption data 12 were illegally copied as they are from the read-only data storage medium 14, by using the read drive.
In that case, the type recognizing section 8 senses that the storage medium to read is not a read-only data storage medium and turns the switch 13 OFF. As a result, the recorded encryption data 12 is not supplied to the decrypting section 10 and the encrypted data 2 is not decoded.
However, not every read drive includes the type recognizing section 8. A read drive with no type recognizing section 8 cannot distinguish recordable data storage media 1 from read-only data storage media 14 and cannot stop the decrypting section 10 from performing its decrypting operation. As a result, such a read drive reads even the data that was copied illegally onto a recordable data storage medium 1.
As is clear from the foregoing description, a read drive with no ability to distinguish recordable data storage media from read-only data storage media reads the encrypted data not just from a read-only data storage medium or a recordable data storage medium, on which the data was written legally, but also from a recordable data storage medium onto which the encrypted data was illegally copied from a read-only data storage medium.
In the field of optical discs, examples of known read-only data storage media include CD-ROMs and DVD-ROMs while examples of known recordable data storage media include CD-Rs, CD-RWs, DVD-Rs, DVD-RWs and DVD-RAMs.
This illegal duplication problem happens not only in optical discs but also in any other type of data storage media that are formatted such that read-only and recordable versions thereof are both readable by the same read drive In order to overcome the problems described above, an object of the present invention is to provide a recordable data storage medium, from which not a read drive with no ability to distinguish recordable and read-only data storage media but just a read drive that guarantees appropriate copyright protection can read user data that was encrypted with property data.
Another object of the present invention is to provide a read drive that prohibits the decrypting section from decoding encrypted data that was illegally copied onto a recordable data storage medium but that allows it to decode legally copied encrypted data.